This invention relates to a heat-developable color light-sensitive material, and more particularly, to a heat-developable color light-sensitive material having retarded sensitivity reduction.
The photographic process using silver halide has heretofore been most widely used because of its improved photographic properties such as sensitivity and gradation control as compared with other photographic processes including electrophotography and diazo process. Recently, an innovative technique was developed which succeeded in readily and fast producing an image in the image forming process of silver halide base light-sensitive materials by replacing the wet treatment using conventional liquid developer by a dry treatment by heating or other suitable means.
Heat-developable light-sensitive materials are well known in the art. The heat-developable light-sensitive materials and their process are described, among others, "Basic Photographic Engineering", Corona Sha (1979), pages 553-555; "Image Information" (April 1978), page 40; Nebletts Handbook of Photography and Reprography, 7th Ed. (Van Nostrand Reinhold Company), page 32; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, and 3,457,075; British Pat. Nos. 1,131,108 and 1,167,777; and Research Disclosure, June 1978, pages 9-15 (RD-17029).
A number of proposals have also been made for producing color images through heat development. One exemplary method for forming color images through coupling of an oxidation product of a developing agent with a coupler and various developing agents used in such a method are disclosed in U.S. Pat. Nos. 3,531,286, 3,761,270, and 4,021,240, Belgian Pat. No. 802,519, and Research Disclosure, September 1975, pages 31-32.
Another heat developing method of incorporating a nitrogen-containing heterocyclic group into a dye to form a silver salt and causing the salt to release the dye through heat development is described in Research Disclosure, May 1978, pages 54-58 (RD-16966).
Also known is a method for forming positive color images by heat-sensitive silver dye bleaching process. For example, Research Disclosure, April 1976, pages 30-32 (RD-14433), idid., December 1976, pages 14-15 (RD-15227), and U.S. Pat. No. 4,235,957 describe useful dye bleaching processes.
Formation of color images using leuco dyes is described in, for example, U.S. Pat. Nos. 3,985,565 and 4,022,617.
These color image producing methods, however, are not satisfactory for an extended period of storage in that color image produced thereby tends to discolor with white areas being colored due to the coexisting silver halide, silver complex, developing agent and the like. To mitigate such an undesirable phenomenon, a number of processes for producing color images through heat development are proposed as diclosed in Japanese patent application Kokai Nos. 57-179840, 57-186774, 57-198458, 57-207250, 58-58543, 58-79247, 58-116537, 58-149046, 59-48764, 59-65839, 59-71046, 59-87450, and 59-88730, etc.
The principal of these processes is that when a light-sensitive silver halide and/or organic silver salt is reduced into silver through heat development, a mobile dye is produced or released in direct or inverse proportion to the reaction. The mobile dye is transferred to a dye fixing element.
These processes, however, have the drawbacks that a substantial sensitivity reduction is likely to occur, particularly when the light-sensitive material is stored for an extended period of time. This phenomenon is outstanding in silver halide emulsions using a sensitizing dye. It is therefore desired to overcome the shelf life or sensitivity reduction problem.